The present invention relates to an ink-jet head using electrostatic force for a driving source for ejecting ink.
An ink-jet head for ejecting ink by pressurization and printing the ejected ink on recording paper has a bubble type which generates a bubble with a heating element to jet ink. In the bubble-type ink-jet head 1, a heating element 5 is provided in a nozzle 3 as shown in FIG. 51 and ink 7 is supplied to the rear part of the nozzle 3 (an upper part in FIG. 51) from an ink cartridge not shown. When the heating element 5 is heated, a bubble 9 is generated in the nozzle 3 and ink pushed out by the bubble 9 is ejected toward recording paper not shown as an ink droplet 7a. When driving voltage is turned off, the bubble 9 disappears, ink 7 flows into the nozzle 3 by capillarity. Repeating it, printing on the recording paper is performed.
An ink-jet head also has a piezoelectric element type using a piezoelectric element and others for a driving source for ejecting ink. In the piezoelectric element-type ink-jet head 11, as shown in FIG. 52, a pin 15 is fixed to the end of a piezoelectric element 13 the base end of which is fixed and the end of the pin 15 is inserted in a nozzle 17. An ink passage 19 is connected to the nozzle 17 and ink 7 is supplied to the ink passage 19 from an ink cartridge not shown. When a driving pulse is applied to the piezoelectric element 13, the piezoelectric element 13 is displaced and the pin 15 is moved in the nozzle 17 so that the ink passage 19 is opened or closed. The ink 7 is sucked by reduced pressure in the nozzle 17 and is ejected as an ink droplet 7a because the pin 15 enters the nozzle 17 again.
However, as the above bubble-type ink-jet head is required to heat ink instantaneously and generate a bubble, there is disadvantage that driving power is large. There is a problem that as time required since a driving pulse is applied to a heating element until a bubble is generated is delayed due to various factors such as the exoergic efficiency of a heating element, thermal conductivity between the heating element (a solid) and ink (fluid) and the temperature dependency characteristics of ink itself, it is difficult to improve the responsibility.
In the meantime, there is disadvantage that in the piezoelectric element-type ink-jet head, high driving voltage is required to acquire physical quantity such as pressure and oscillation. There is also a problem that the sensitivity of conversion is relatively low and it is thus Difficult to improve the responsibility. Further, there is a problem that as the ink-jet head is required to have resonant structure with deforming material if the ink-jet head is integrated with the deforming material, the design is difficult. It is also expected that the ink-jet head is connected to an electronic circuit to be an integrated circuit by forming a piezoelectric element on the same substrate, however, in this case, there is a problem that micronization and integration is difficult by a method of forming a thick film and the formation of a piezoelectric film itself is difficult by a method of forming a thin film.
To solve such problems, there is proposed an ink-jet head wherein ink is ejected by deforming a diaphragm wall, which constitutes a part of an ink chamber, by electrostatic force (Maxwell stress).
For example, U.S. Pat. No. 4,520,375 discloses an ink-jet head wherein ink is ejected by providing a parallel flat diaphragm made of a semiconductor on one side of an ink chamber and pressurizing after reducing pressure by electrostatic force.
Unexamined Japanese Patent Publication No. Hei 5-50601 discloses an ink-jet head provided with plural nozzle apertures, plural ejecting chamber communicating with each nozzle aperture and a diaphragm for deforming a part of the ejecting chamber wherein ink is ejected by deforming the diaphragm with electrostatic force so that the ejecting chamber is under reduced pressure and pressurizing the ejecting chamber when the diaphragm is restored afterward.
Unexamined Japanese Patent Publication No. Hei 6-106725 discloses an ink-jet head wherein ink is ejected from the end of a nozzle by forming a nozzle with a rigid electrode and an elastic electrode opposite, making ink with a high dielectric constant flow into the nozzle and applying voltage between both electrodes to deform the elastic electrode in the direction of the rigid electrode with electrostatic attraction.
The ink-jet heads according to these methods have advantages that driving voltage can be reduced, compared with the above bubble-type and the above piezoelectric element type, high speed driving is enabled, large scale integration is enabled, the degree of freedom in selecting the material of the element is high, the design is easy and in addition, a driving circuit can be integrated by forming the ink-jet head with a semiconductor such as silicon.
However, for these ink-jet heads, means for achieving high speed ejecting and efficient ejecting is not referred. The control of gradation and the correction of the quantity of ink when multiple nozzles are provided are also not referred.
There are the following problems to realize the above high speed ejecting and the above efficient ejecting:
That is, in an ink chamber, an ink ejection port and an ink supply port exist. There occurs a problem that as simultaneously, ink reversely flows toward a reservoir from the ink supply port if the ink chamber is pressurized and ink is ejected from the ink ejection port, energy efficiency for ejecting ink is bad (efficient ejecting cannot be executed) and ink cannot be ejected at high speed. To solve the problem, the passage resistance of the ink supply port is required to be set to a higher value, compared with that of the ink ejection port.
In the meantime, there occurs a problem that when the passage resistance of an ink supply port is high if an ink chamber is decompressed and ink is supplied from the ink supply port, ink supply speed is reduced and ink cannot be supplied at high speed. In this case, bubbles may invade from an ink ejection port. To solve the problem, the passage resistance of the ink supply port is required to be reduced, compared with that of the ink ejection port.
Since these conditions conflict with each other, in the related arts, a neutral value is acquired based upon both compromised values and the passage resistance of an ink supply port and an ink ejection port is determined.
To solve such a problem, Unexamined Japanese Patent Publication No. Hei 9-141855 discloses an ink-jet head wherein an ink supply port is tapered, however, there is a limit in effect because passage resistance is controlled every direction in which ink flows, depending upon only the shape of a passage.
There are the following problem in relation to the control of gradation:
That is, heretofore, there has been known a method of controlling the gradation by varying directly the concentration or the area of an ink droplet to vary the quantity of ejected ink by means of controlling the degree of pressurization (value, applied time, or the number of pulses of voltage). However, in the case of an ink-jet head, as the volume of an ink chamber is very large, compared with the volume of a ejected ink droplet, it is difficult to control the quantity of an ink droplet precisely.
To solve these problems, Unexamined Japanese Patent Publication No. Hei 9-193385 discloses an ink-jet head wherein the control of gradation and correction in ejecting from plural nozzles are enabled by means of pressurizing by a single piezoelectric element and plural buckled valve means based upon generated heat. However, pressurizing by a piezoelectric element has a problem that a response is slow as described above and driving voltage is high. A built-in assembly of a piezoelectric element costs high and is not suitable for large scale integrated multi-nozzle. The buckled valve depends upon thermal expansion, is slow in a response, and the reliability and the life are also questionable. Further, as one pressurizing member makes ink ejected from plural nozzles, correction is required. For the correction of the quantity of ink in the case of multi-nozzle, there are the following problem:
That is, a multi-nozzle-type head provided with plural ink chambers communicating with a reservoir has a problem that the high quality of ink ejecting cannot be obtained because of interference between adjacent nozzles.
To solve such a problem, Unexamined Japanese Patent Publication No. Hei 5-193149 discloses an ink-jet head wherein a valve is provided to the end of a nozzle (an ink supply port) to prevent interference between adjacent nozzles. However, pressurizing member depends upon a bubble (thermal bubble) method, and speedup and the reliability are questionable. The structure of the valve and the assembly are complicated. Further, the object of the structure is to prevent interference between adjacent nozzles and is not high speed ejecting and the control of gradation.
The present invention is made in view of the above situation and a first object is to obtain an ink-jet head wherein high speed responsibility can be obtained with low voltage.
Further, a second object is to obtain an ink-jet head wherein high speed ejecting and efficient ejecting are enabled.
Furthermore, a third object is to obtain an ink-jet head wherein the high quality of the control of gradation by varying the quantity of ink is enabled.
Furthermore, a fourth object is to obtain an ink-jet head wherein integration is enabled by a photolithographic process, the degree of the freedom of design can be enhanced, in addition, an integrated circuit is realized, and micronization and multiplicity are easy.
In order to achieve the above object, there is provided an ink-jet head comprising: at least one ink chamber having an ink supply port and an ink ejection port; a flexible member constituting a part of one inner wall of the ink chamber; a signal electrode provided on the flexible member; a common electrode provided where is opposed to the signal electrode with void defined therebetween; a power supply section for applying driving voltage between the signal electrode and the common electrode in accordance with print information to elastically deform the flexible member toward the common electrode by electrostatic force acting therebetween.
In the ink-jet head, as a flexible member is operated utilizing the electrostatic force, the high speed operation is enabled, compared with a case that a heating element or a piezoelectric element is used.
The elastic deformation of the flexible member pressurizes the ink chamber.
In the ink-et head, when voltage is applied between the common electrode and the signal electrode, the flexible member is attracted by Coulomb""s force and bent, and ink in the ink chamber is ejected from the ink ejection port as an ink droplet. When voltage is turned off, the flexible plate is elastically restored, the ink chamber is decompressed and ink flows from the ink supply port to get ready for ejecting the next ink droplet.
The elastic deformation of the flexible member may decompress the ink chamber.
In the ink-jet head, when voltage is applied between the common electrode and the signal electrode, the flexible member is attracted by Coulomb""s force and bent, and ink is supplied into the ink chamber from the ink supply port. When voltage is turned off, the flexible plate is elastically restored, the ink chamber is pressurized and ink in the ink chamber is ejected from the ink ejection port as an ink droplet.
A plurality of the ink chamber may be arranged on one band-like common electrode in the longitudinal direction thereof, and the power supply section selectively applies the drive voltage to the respective signal electrode provided on each of the flexible member in accordance with the print information.
In the ink-jet head, multiplicity in which an ink droplet is ejected from a desired ink chamber by selectively applying the driving voltage to each signal electrode based upon the printing information is enabled.
The ink-jet head may further comprise: a flexible valve member provided inside the ink chamber, the flexible valve member placed in the vicinity of at least one of the ink supply port and the ink ejection port; a valve electrode provided on the flexible valve member; a valve drive power supply section for applying valve driving voltage between the valve electrode and the common electrode in accordance with the print information to elastically deform the flexible valve member toward the common electrode by electrostatic force acting therebetween.
In the ink-jet head, the flexible member deformed by the electrostatic force serves as a pressure generating member the pressure generating member and the flexible valve member deformed by the same serves as a valve for the ink supply port and the ink ejection port. Thus, both of the pressure generating member and the valve can be produced with simple structure.
The flexible valve member may be deformed in a direction which is substantially perpendicular to an ink flowing direction.
In the ink-jet head, the flow of ink is not perpendicular to the surface of the valve and the valve can be opened or closed with small force without being influenced by the flow of ink.
The flexible valve member may be deformed in a direction which is substantially parallel to an ink flowing direction.
In the ink-jet head, as the ink ejection port or the ink supply port is opened or closed by the surface of the valve, the relatively large area of the opening can be securely opened or closed.
In case the flexible valve member is provided in the vicinity of the ink ejection port, and the ink chamber is pressurized when the driving voltage is applied, a numerical aperture of the ink ejection port is reduced by the valve member after the ink is ejected therefrom and then the application of the drive voltage by the power supply section is terminated.
In the method of driving the ink-jet head, as the numerical aperture of the ejection port is reduced when ink is supplied, reduced pressure operating upon the ink chamber is focused upon the ink supply port and efficient ink supply with few pressure loss is enabled.
In case the flexible valve member is provided in the vicinity of the ink supply port, and the ink chamber is pressurized when the driving voltage is applied, a numerical aperture of the ink supply port is reduced by the valve member after the ink is supplied therefrom and then the application of the drive voltage by the power supply section is started.
In the method of driving the ink-jet head, pressure upon the ink chamber is focused upon the ink ejection port by reducing the numerical aperture of the ink supply port when ink is ejected and efficient ink ejecting with few pressure loss is enabled.
In case the flexible valve members are provided both of in the vicinity of the ink supply port and in the vicinity of the ink ejection port, and the ink chamber is pressurized when the driving voltage is applied, a numerical aperture of the ink supply port is closed by the valve member after the ink is supplied therefrom and then the application of the drive voltage by the power supply section is started, and a numerical aperture of the ink ejection port is closed by the valve member after the ink is ejected therefrom and then the application of the drive voltage by the power supply section is terminated.
In the method of driving the ink-jet head, efficient ink ejecting with few pressure loss is enabled by reducing the numerical aperture of the ink supply port when ink is ejected and efficient ink supply with few pressure loss is enabled by reducing the numerical aperture of the ink ejection port when ink is supplied.
In case the flexible valve member is provided in the vicinity of the ink ejection port, and the ink chamber is decompressed when the driving voltage is applied, a numerical period of the ink ejection port is reduced by the valve member after the ink is ejected therefrom and then the application of the drive voltage by the power supply section is started.
In the method of driving the ink-jet head, as the numerical aperture of the ejection port is reduced when ink is supplied, reduced pressure operating upon the ink chamber is focused upon the ink supply port and efficient ink supply with few pressure loss is enabled.
In case the flexible valve member is provided in the vicinity of the ink supply port, and the ink chamber is decompressed when the driving voltage is applied, a numerical aperture of the ink supply port is reduced by the valve member after the ink is supplied therefrom and then the application of the drive voltage by the power supply section is terminated.
In the method of driving the ink-jet head, pressure upon the ink chamber is focused upon the ink ejection port by reducing the numerical aperture of the ink supply port when ink is ejected and efficient ink ejecting with few pressure loss is enabled.
In case the flexible valve members are provided both of in the vicinity of the ink supply port and in the vicinity of the ink ejection port, and the ink chamber is decompressed when the driving voltage is applied, a numerical aperture of the ink ejection port is reduced by the valve member after the ink is ejected therefrom and then the application of the drive voltage by the power supply section is started, and a numerical aperture of the ink supply port is reduced by the valve member after the ink is supplied therefrom and then the application of the drive voltage by the power supply section is terminated.
In the method of driving the ink-jet head, efficient ink ejecting with few pressure loss is enabled by reducing the numerical aperture of the ink supply port when ink is ejected and efficient ink supply with few pressure loss is enabled by reducing the numerical aperture of the ink ejection port when ink is supplied.
The valve drive power supply section may apply the valve drive voltage so the flexible valve member as to deform to vary a numerical aperture of the associated port.
In the method of driving the ink-jet head, the quantity of ejected ink can be arbitrarily controlled by changing the numerical aperture of at least one of the ink ejection port and the ink supply port, and the representation of gradation is enabled.
The valve drive power supply section may apply the valve drive voltage so the flexible valve member as to deform to vary a reduction period of a numerical aperture of the associated port.
In the method of driving the ink-jet head, the quantity of ejected ink can be arbitrarily controlled by varying the reduction period for at least one of the ink ejection port and the ink supply port, and the representation of gradation is enabled.
The common electrode may be divided into a first common electrode portion opposing to the signal electrode and a second common electrode portion opposing to the valve electrode.
In the ink-jet head, electric field crosstalk between electrodes can be reduced and the ink-jet head can be more precisely operated.
The ink-jet head may further comprise: a common reservoir communicated with a plurality of the ink chambers arranged on one band-like common electrode in the longitudinal direction thereof, wherein the power supply section selectively applies the drive voltage to the respective signal electrode provided on each of the flexible member in accordance with the print information, and the valve drive power supply section selectively applies the valve drive voltage to the respective valve electrode provided on each of the flexible valve member in accordance with the print information.
In the method of driving the ink-jet head, even if the plural ink chambers communicate with the reservoir, each pressure of adjacent ink chambers never interferes by controlling opening or closing a valve provided to the ink ejection port or the ink supply port every ink chamber, and efficient ink ejecting and efficient ink supply are enabled even in the multi-nozzle head.
Furthermore, the plural ink chambers can be integrated by photolithography, etching and others. As the valve is provided to at least one of the ink ejection port and the ink supply port, each pressure of adjacent ink chambers never interferes even if the adjacent ink chambers respectively communicate with the reservoir.
At least the common electrode, the ink chamber, the flexible member and the signal electrode are formed so as to be subsequently laminated by a photolithographic process.
In the ink-jet head, the main part such as the ink chamber can be formed in the photolithographic process, and the integration of the main part, micronization, the realization of an integrated circuit and multiplicity are easy.
The flexible member and the flexible valve member are one of a conductor and a conductor at least a part of over which is covered with insulator.
In the ink-jet head, large electrostatic force can be obtained by composing the flexible member and the flexible valve member of an electric conductor, and a short circuit and field emission can be prevented by covering an electric conductor with an insulator.
An ink-jet head disclosed in claim 4 is based upon an ink-jet head provided with an ink chamber having an ejection port and an ink supply port and pressure generating member provided to the ink chamber and characterized in that the ink chamber is pressurized or decompressed by deforming the pressure generating member with electrostatic force and ink in the ink chamber is ejected from the ejection port as an ink droplet, and is characterized in that a valve for arbitrarily changing the numerical aperture of the ejection port with electrostatic force is provided to the ink chamber.
In the ink-jet head, ink can be efficiently supplied from the ink supply port by closing the ejection port in supplying ink. An ejecting cycle can be reduced and high speed ejecting is enabled.
An ink-jet head disclosed in claim 5 is based upon an ink-jet head provided with an ink chamber having an ejection port and an ink supply port and pressure generating member provided to the ink chamber and characterized in that the ink chamber is pressurized or decompressed by deforming the pressure generating member with electrostatic force and ink in the ink chamber is ejected from the ejection port as an ink droplet, and is characterized in that a valve for arbitrarily changing the numerical aperture of the ink supply port with electrostatic force is provided to the ink chamber.
In the ink-jet head, pressurized ink can be efficiently ejected by closing the ink supply port in ejecting ink, an ejecting cycle can be reduced and high speed ejecting is enabled.
An ink-jet head disclosed in claim 6 is based upon an ink-jet head provided with an ink chamber having an ejection port and an ink supply port and pressure generating member provided to the ink chamber and characterized in that the ink chamber is pressurized or decompressed by deforming the pressure generating member with electrostatic force and ink in the ink chamber is ejected from the ejection port as an ink droplet, and is characterized in that a valve for arbitrarily and independently changing the numerical aperture of the ejection port and the ink supply port with electrostatic force is provided to the ink chamber.
In the ink-jet head, ink can be efficiently supplied from the ink supply port by closing the ejection port in supplying ink, pressurized ink can be efficiently ejected by closing the ink supply port when ink is ejected, an ejecting cycle is remarkably reduced and high speed ejecting is enabled.
An ink-jet head disclosed in claim 8 is characterized in that a valve is moved or turned with electrostatic force.